Isonitrile complexes of a number of radionuclides that are useful as radiopharmaceuticals are described by Jones et. al. in U.S. Pat. No. 4,452,774. The complexes are described as being useful for visualizing cardiac tissue, detecting the presence of thrombi in the lungs and other types of blood perfusion defects, studying lung function, studying renal excretion and imaging the bone marrow and the hepatobiliary system. In practice, however, these complexes containing simple hydrocarbon isonitrile ligands have moderately high uptake in the lungs and liver of humans. See, e.g., Holman et. al., J. Nucl. Med. 25, 1380 (1984). This uptake can interfere with the visualization of cardiac tissue.
The problem of lung and liver uptake can be partially overcome by using the isonitrile complexes described by Jones et. al. in U.S. Pat. Nos. 4,735,793 and 4,872,561. These ester or amide isonitrile complexes generally give better lung and liver clearance, thus allowing earlier or higher contrast imaging. A superior series of ether-substituted isonitrile complexes are described by Bergstein and Subramanyan in U.S. Pat. No. 4,988,827. These ether-substituted isonitrile complexes have been extensively evaluated in vivo. Clinical evaluations of technetium-99m (Tc-99m) ether-substituted isonitrile complexes are reported in Kahn et. al., Circulation, 79, 1282-1293 (1989); Iskandriam et. al., Amer. J. Cardiol. 64, 270-275 (1989); and Christian et. al., Circulation 83, 1615-1620 (1991).
The development of a process for the commercial manufacture of lyophilized kits for the preparation of Tc-99m isonitrile complexes was complicated by the volatility of the isonitrile ligands. Carpenter, Jr. et. al. described in U.S. Pat. No. 4,894,445 a solution to this problem by the synthesis of isonitrile adducts of non-radioactive metals such as Cu, Mo, Pd, Co, Ni, Cr, Ag and Rh. The metal-isonitrile adducts are chosen so that when combined with a radioactive metal in an appropriate media, the metal will be displaced by the radioactive metal to form the desired radiopharmaceutical. The copper complexes described are bis(isonitrile)phenanthroline and tetrakis(isonitrile) complexes. Many such adducts react with the desired metal radionuclide (e.g., Tc-99m) at elevated temperature to produce the radiopharmaceutical relatively rapidly. However, the heating requirement is inconvenient and cumbersome in the hospital setting.
Iqbal et. al. describe in U.S. Pat. No. 4,885,100 tris(isonitrile)copper(I) adducts with an anion selected from BF.sub.4, PF.sub.6, ClO.sub.4, I, Br, Cl and CF.sub.3 COO. These adducts react with radionuclides, such as Tc-99m, and provide more rapid preparation of radiopharmaceuticals at room temperature than the complexes described by Carpenter, Jr. et. al. However, the technology described by Iqbal et. al. does not give sufficiently high yields of Tc-99m-isonitrile complexes after sufficiently short time periods to be practical in a busy hospital setting.
Consequently, a need exists for facile, efficient and cost-effective reagents and methods for preparation of radionuclide complexes.